As the U.S. and its allies furiously work to train thousands more troops for the daunting task of retaking Iraq's second largest city, Islamic State fighters are waging a diversion campaign of bloody suicide attacks in Baghdad and elsewhere. Their aim is to force Iraq's already overburdened security forces to spread even thinner to protect the capital and other cities rather than prepare the Mosul operation.

Iraq's answer to that has been a plan to build a wall around the capital. Meanwhile, the U.S.-led coalition and the Iraqis are struggling to protect pockets of territory that have been recaptured from the extremists.

"Mosul will be very complicated, it will be a mix of forces and it will be very important to ensure it's well planned," Brett McGurk, President Barack Obama's envoy to the U.S.-led coalition fighting IS, said Saturday.

U.S. Army Col. Christopher Garver, a coalition spokesman, put it more bluntly. "The forces that are going to conduct that assault into the city, they're not in place yet."

The northern city of Mosul, once home to more than a million people, was the biggest prize captured by IS when it swept over much of Iraq's north and west in the summer of 2014 and declared a "caliphate" across those lands and territory it holds in Syria. While Iraqi forces have clawed back some territory in the past year, retaking Mosul is considered crucial for breaking the jihadis' back in the country. Estimates of the number of IS fighters in Mosul vary from a few thousand to "not more than 10,000," according to the coalition.

The Iraqi military is still struggling to regroup. When Mosul fell to IS, more than a third of the military disintegrated as thousands of soldiers shed their uniforms and dropped their weapons to flee. In the following months, tens of thousands more Iraqi troops were identified as "ghost soldiers" -- nonexistent troops whose pay was pocketed by commanders.

The U.S.-led coalition began a training program months later in December 2014, but so far only 18,500 soldiers and security forces have been trained in courses which last around seven weeks. Experts question whether such a crash course is adequate preparation. Coalition and Iraqi officials estimate eight to 12 brigades, or an estimated 24,000 to 36,000 troops, will be needed for the operation to capture Mosul.

So far, 2,000 to 3,000 Iraqi troops have been deployed at Makhmour base, the likely staging ground for a Mosul assault, located 40 miles (67 kilometers) southeast of the city.

"We are all trained, qualified and ready for battle. But this force is not enough to retake Mosul," said Iraqi Lt. Col Mohammed al-Wagaa, stationed at Makhmour. "The battle for Mosul is going to take a long time."

Under political pressure to show victory, al-Abadi has repeatedly vowed to "liberate" Mosul this year. But U.S. Lt. Gen. Vincent Stewart, head of the Defense Intelligence Agency, told Congress last month: "I'm not as optimistic."

Stewart said they may be able to begin "isolation operations" around the city, but "securing or taking Mosul is an extensive operation and not something I see in the next year or so."

The Iraqi military's few competent, battle-tested units are scattered, helping to hold various front lines against IS in the country's central and western provinces or tied down controlling cities and towns retaken from the militants since other security forces aren't capable.

Iraq's elite counterterrorism forces have units near Tikrit and Baiji in central Iraq and Habaniya in the west. In Ramadi, capital of the western Anbar province, a counterterrorism commander said his unit has to remain because local police forces can't maintain control. He spoke on condition of anonymity because he's not authorized to talk to the press.

"You can't just pick up and leave," Garver said. Without proper forces in place, "Daesh comes back in and seizes terrain that you just spent months taking from them," he said, using an Arabic acronym for IS.

IS has meanwhile stepped up attacks on Baghdad and other towns removed from front-line fighting. Over the past week a double bombing at a market in Baghdad's Sadr City killed more than 70 people. The following day, a suicide attack at a funeral north of Baghdad killed over 30, and on Sunday an explosives-laden fuel truck plowed into a checkpoint south of the capital, killing at least 47 people and wounding dozens.

The attacks likely aim at delaying deployment of troops to Makhmour or along the Euphrates River valley for the Mosul assault by forcing the military to move its best forces to protect the capital, said Patrick Martin, an Iraq analyst at the Washington-based Institute for the Study of War.

So far the attacks haven't slowed deployments north. But "if it becomes really bad and multiple attacks like these happen in the near future, (the military's) calculus will probably have to shift," Martin said.

Last month security officials announced work had begun on a 280 kilometer (175 mile) "wall" around Baghdad that would reduce militant attacks inside the city. The Interior Ministry said it would be a combination of tightened checkpoints, trenches and blast walls completely surrounding the capital.

The military must also clear IS fighters from more than 100 kilometers (70 miles) of territory to ensure reliable supply lines between Makhmour and Baghdad, said a Baghdad-based military commander overseeing preparations for the Mosul offensive. He spoke on condition of anonymity as he was not authorized to brief the press.

Politics have also complicated planning efforts.

"No one has the right to prevent us from participating in the liberation of the city of Mosul," Abu Mahdi al-Mohandes, the head of the government-sanctioned Popular Mobilization Forces, mostly made up of Shiite militias, said at a Thursday press conference.

Shiite militiamen -- some of the most effective ground forces against IS -- led the fight to retake the mainly Sunni city of Tikrit and were accused of human rights violations in the process. The U.S.-led coalition has repeatedly refused to launch airstrikes in support of Shiite militia operations. In last summer's Anbar offensive, the PMF stood aside and heavy coalition airstrikes proved decisive in Iraqi military gains there.

"We will rely on ourselves in the fighting," Maj. Gen. Bahaa al-Azzawi, chief of police in Mosul's Nineveh province, told the AP. "But if we get support from the coalition, this will reduce how long it will take to liberate (Mosul). It will speed up the process and reduce our losses."